Synchronization is an important task in any communication receiver. In a digital receiver, samples of the signal at symbol points (time instants) should be taken accurately and provided to a decision device, such as a Quantizer or Viterbi Decoder. Any substantial deviation or drift in the sampling instant should be tracked and corrected where possible by a timing recovery mechanism. This task of timing recovery may be difficult for multilevel modulation schemes such as Quadrature Amplitude Modulation (QAM) schemes, such as 16-QAM, 64-QAM, 256-QAM, etc.
One algorithm for timing error detection is presented in F. M. Gardner, “A BPSK/QPSK timing-error detector for sampled receivers” IEEE Trans. Comm., Vol. COM-34, no. 5, pp. 423-429, May, 1986. However, this type of timing error detector is useful only for measuring timing errors for modulation schemes in which the absolute value of symbol amplitudes remain constant, such as for Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK), for example. There is a need for a timing error detector that can measure timing error for modulation schemes in which multiple levels or multiple amplitudes are used, such as QAM modulation schemes.